A microwave multiple-input multiple-output (Multiple-Input Multiple-Out-put, MIMO) system may effectively increase spectrum utilization in wireless communication. Different from the wireless MIMO, the microwave MIMO adopts distributed outdoor units (OutdoorUnit, ODU) to transmit signals. The distributed ODUs are independent ODUs in each branch of multiple paths, with independent device parameters such as frequency offset and phase noise of each branch. Therefore, each branch has different frequency offset components.
The conventional MIMO frequency offset estimation method and channel estimation method consider only the case that the frequency offsets are consistent. When the conventional method is used to perform frequency offset estimation on the distributed microwave MIMO system, the frequency offset estimation result is inaccurate. In addition, due to inconsistency between the frequency offsets of ODUs, the channel estimation result includes residual frequency offset information and is also inaccurate. Therefore, the conventional MIMO frequency offset estimation method and channel estimation method are not applicable to the frequency offset estimation and the channel estimation in the distributed microwave MIMO system.